linux-kernel - Re: [PATCH 2/6] drivers base/arch_topology: frequency-invariant load-tracking support

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Date:   Wed, 21 Jun 2017 17:40:51 +0100
From:   Dietmar Eggemann <dietmar.eggemann@....com>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        "linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
        Russell King - ARM Linux <linux@....linux.org.uk>,
        LAK <linux-arm-kernel@...ts.infradead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Russell King <rmk+kernel@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Juri Lelli <juri.lelli@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH 2/6] drivers base/arch_topology: frequency-invariant
 load-tracking support

On 14/06/17 14:08, Vincent Guittot wrote:
> On 14 June 2017 at 09:55, Dietmar Eggemann <dietmar.eggemann@....com> wrote:
>>
>> On 06/12/2017 04:27 PM, Vincent Guittot wrote:
>>> On 8 June 2017 at 09:55, Dietmar Eggemann <dietmar.eggemann@....com> wrote:

[...]

>>
>> Yes, we should free cpus_to_visit if the policy notifier registration
>> fails. But IMHO also, once the parsing of the capacity-dmips-mhz property
>> is done. free cpus_to_visit is only used in the notifier call
>> init_cpu_capacity_callback() after being allocated and initialized in
>> register_cpufreq_notifier().
>>
>> We could add something like this as the first patch of this set. Only
>> mildly tested on Juno. Juri, what do you think?
>>
>> Author: Dietmar Eggemann <dietmar.eggemann@....com>
>> Date:   Tue Jun 13 23:21:59 2017 +0100
>>
>>     drivers base/arch_topology: free cpumask cpus_to_visit
>>
>>     Free cpumask cpus_to_visit in case registering
>>     init_cpu_capacity_notifier has failed or the parsing of the cpu
>>     capacity-dmips-mhz property is done. The cpumask cpus_to_visit is
>>     only used inside the notifier call init_cpu_capacity_callback.
>>
>>     Reported-by: Vincent Guittot <vincent.guittot@...aro.org>
>>     Signed-off-by: Dietmar Eggemann <dietmar.eggemann@....com>
> 
> your proposal for freeing cpus_to_visit looks good for me
> 
> Acked-by: Vincent Guittot <vincent.guittot@...aro.org>

Thanks.

[...]

>> IMHO, that's not necessary.
>>
>> The transition notifier works completely independent from the policy
>> notifier. In case the latter gets registered correctly and the registration
>> of the former fails, the notifier call of the policy notifier still parses
>> the capacity-dmips-mhz property information and sets per_cpu(max_freq, cpu).
>>
>> The notifier call set_freq_scale_callback() of the transition notifier will
>> not be called so that frequency invariance always returns
>> SCHED_CAPACITY_SCALE.
>>
>> After the policy notifier has finished its work, it schedules
>> parsing_done_work() in which it gets unregistered.
> 
> Ok so IIUC, the transition notifier is somehow optional and we still
> have the cpu invariance.
> In this case, you should not return the error code of
> cpufreq_register_notifier(&set_freq_scale_notifier,
> CPUFREQ_TRANSITION_NOTIFIER) as the error code of the
> register_cpufreq_notifier function.
> you should better print a warning like " failed to init frequency
> invariance" and return 0 for register_cpufreq_notifier()

Makes sense. Will change this.

[...]